Devices for imaging body cavities or passages in vivo are known in the art and include endoscopes and autonomous encapsulated cameras. Endoscopes are flexible or rigid tubes that pass into the body through an orifice or surgical opening, typically into the esophagus via the mouth or into the colon via the rectum. An image is formed at the distal end using a lens and transmitted to the proximal end, outside the body, either by a lens-relay system or by a coherent fiber-optic bundle. A conceptually similar instrument might record an image electronically at the distal end, for example using a CCD or CMOS array, and transfer the image data as an electrical signal to the proximal end through a cable. Endoscopes allow a physician control over the field of view and are well-accepted diagnostic tools.
Capsule endoscope is an alternative in vivo endoscope developed in recent years. For capsule endoscope, a camera is housed in a swallowable capsule, along with a radio transmitter for transmitting data, primarily comprising images recorded by the digital camera, to a base-station receiver or transceiver and data recorder outside the body. The capsule may also include a radio receiver for receiving instructions or other data from a base-station transmitter. Instead of radio-frequency transmission, lower-frequency electromagnetic signals may be used. Power may be supplied inductively from an external inductor to an internal inductor within the capsule or from a battery within the capsule.
An autonomous capsule camera system was disclosed in the U.S. Pat. No. 8,636,653, entitled “In vivo camera with multiple sources to illuminate tissue at different distances” granted on Jan. 28, 2014. One embodiment disclosed in U.S. Pat. No. 8,636,653 uses multiple electromagnetic radiation sources to illuminate surface of an organ (e.g. the mucosa surface of intestines) so that images can be captured from the light that is scattered off of the surface. FIG. 1 illustrates an example of use of an endoscope having two light emitters, for illumination and imaging over short distances. Specifically as illustrated in FIG. 1 on the right side, mucosa surface 101 at points F and G which is close to (e.g. <5 mm) or touching endoscope 100, is illuminated by light emerging from a compound parabolic concentrator (CPC) 113, both directly and after reflection from reflector 118. In the illustrative embodiment shown in FIG. 1, reflector 118 enables light from an emitter in short-range source 103 to reach an illumination region of the endoscope from both sides of the field of view, thereby to illuminate tissue surface 101 more uniformly in an image to be diagnosed, as compared to short-range illumination from only one side of the field of view.
Additionally, a tissue surface 101 located at point H which is in contact with endoscope 100 is also illuminated by light emerging from surface 114 which light entered CPC 113 through a bottom surface as described above, and is reflected by a convex surface in CPC 1100. As tissue surface 101 is in contact with inside of endoscope housing 102, point H is outside the FOV of the camera. However, as the distance increases, point H falls within the FOV. Accordingly, endoscope 100 uses a minimum amount of energy, e.g. by using primarily just a single LED within short-range source 103 in the direction towards the right of FIG. 1.
Note that endoscope 100 of these embodiments includes an additional LED used for long-range sources (104, 107) that, when turned on, also provides light in the same radial direction, i.e. towards the right and left of FIG. 1. Long-range sources (104, 107) are positioned longitudinally offset from the objective's optical axis, e.g. positioned behind mirror 118 which acts as a baffle. Note that there is little or no overlap between the long-range illumination regions on the endoscope's tubular wall (close to point E in FIG. 1) lit up by light source 104, and the above-described short-range illumination region lit up by light source 103. The area of long-range illumination region lit up by light source 104 is several times and in some cases an order of magnitude, smaller than the corresponding area of short-range illumination region lit up by light source 103.
Endoscope 100 increases the radiant energy generated by the long-range light source 104 as the distance of the tissue to be imaged increases. Using long-range light source 104 simultaneously with short-range light source 101 provides sufficient illumination to image mucosa 101 that is located far away (e.g. ˜20 mm away). For example, points A-D shown on the left side of FIG. 1 are illuminated by turning on both light sources 106 and 107.
Use of both light sources 106 and 107 does use up a maximum amount of energy (relative to use of just one source 106), although such use provides better images which enable a more thorough diagnosis of a body cavity, such as a gastrointestinal tract. The energy generated by multiple light sources 103 and 104 to illuminate radially in a given direction may be scaled appropriately, to illuminate tissue located at intermediate distance(s). Accordingly, endoscope 100 in some embodiments of the invention operates multi-modally, specifically in a minimum energy mode, a maximum energy mode and one or more intermediate energy modes. For certain body cavities, such as a small intestine, endoscope 100 of these embodiments operates continuously in a minimal mode, by turning on only the short-range source, e.g. source 103 (i.e. the long-range source is kept turned off).
Note that endoscope 100 of FIG. 1 incorporates four objectives with optical axes spaced 90° apart, although only two lenses 111 and 112 that are oppositely directed are shown in FIG. 1. In this example, eight LEDs are arrayed in a ring under an annular truncated CPC 113. The eight LEDs emit out the outer surface 114 of CPC 113 and also through the top of the CPC apertures A2 (not labeled in FIG. 1). Some of the light from aperture A2 is reflected down and out of the endoscope 100 by annular mirror 118 located above the imaging region. In FIG. 1, the angle of the mirror 118 relative to the optical axis is chosen such that the reflected light satisfies the relationship θr<θ2 where θ2 is the maximum angle of light exiting the CPC cavity in the radial direction and θr is the angle of a ray reflected from the annular mirror relative to an inner or outer surface of the tubular wall.
The sensor, sources and optical elements in the capsule endoscope are properly arranged to avoid overlaps between long-range illumination region and imaging region as well as between short-range illumination region and imaging region so as to eliminate or reduce any possibility that a virtual image (also called “ghost”), due to long-range light or the short-range light reflected by housing 102, is present in an image that is captured by the camera and used for diagnosis. The ghost-forming light passes from the source to the housing directly or indirectly, in the latter case first scattering off objects within the capsule housing. Also, the housing has a transparent region (window) and image-forming rays enter the housing at the same location in the transparent region from which ghost-forming light reflects/scatters. A ghost forming ray is collinear with an image-forming ray originating outside the capsule. Image forming rays are formed by light from objects outside the housing illuminated by the light source. In practice, the proper arrangement of sources and optical elements in the capsule endoscope has helped to substantially reduce the ghosts. Nevertheless, certain degrees of ghosts are still visible in the captured images. The ghosts typically occur when light from short-range sources scatters off of surfaces inside the capsule housing and then reflects from the housing into a camera objective. In order to eliminate a ghost from reflection of long-range light or short-range light by the housing, one solution is to have the sensor operated to exclude the ghost e.g. by cropping the image. During cropping, only a part of an image in a central region thereof is transmitted by endoscope 100 to a computer for use in diagnosis by excluding the rest of the image containing the ghost. Alternatively, the full-size images can be transmitted to the computer and the cropping can be done by the computer. While this method is simple, some imaging areas have to be sacrificed.
Accordingly it is desirable to develop techniques to eliminate ghosts without the need for sacrificing valuable imaging areas.